Smartform Runtime Error CX_SY_CONVERSION_NO_NUMBER

On SAP Form Builder I got runtime error CONVT_NO_NUMBER due to CX_SY_CONVERSION_NO_NUMBER exception on SAPLSTXK ABAP program while editing SAP Smartform using smartforms transaction.

After a search on Google, I found that there are two SAP Notes related with this issue:
SAP Note 827715 - CSV 1.0: CX_SY_CONVERSION_NO_NUMBER short dump, and
SAP Note 1452849

Implementing SAP Note 1452849 will solve the SAP Smartform dump error

Error in the ABAP Application Program
The current ABAP program "SAPLSTXK" had to be terminated because it has come across a statement that unfortunately cannot be executed.

Error analysis
An exception occurred that is explained in detail below.
The exception, which is assigned to class 'CX_SY_CONVERSION_NO_NUMBER', was not caught in procedure "RTF_SET_PATTERN" "(FORM)", nor was it propagated by a RAISING clause.
Since the caller of the procedure could not have anticipated that the exception would occur, the current program is terminated.
The reason for the exception is:
The program attempted to interpret the value "15&gv_maktx&" as a number, but since the value contravenes the rules for correct number formats, this was not possible.